1. Field of the Invention
The present invention relates to a device for reproducing received data and a method of adjusting frequency therefor. More particularly, a received data reproducing device in accordance with the present invention is applied to radio data communication and may be implemented as a baseband receiver based on Bluetooth (trade name), which is a specific radio communication standard, or a receiver arrangement configured to receive the baseband signal of serial data by way of example. Also, a frequency adjusting method in accordance with the present invention optimizes a clock frequency used to sample a received baseband signal for thereby producing optimum phase information by sampling.
2. Description of the Background Art
A received data reproducing device of the type using Bluetooth uses a clock higher than the symbol rate of the received data to separate a received sample clock and reproduce received data. With such a clock, the reproducing device detects, among received data, a synchronizing word heading the data and serving as a clue to synchronization and estimates the phase of a point or position where a data value varies, i.e. a data transition point. By using the result of the estimation, the reproducing device separates the clock component of the received data, fixes the phase, and uses the resulting signal as a clock for sampling the received data.
To cope with sharp phase changes and noise that may occur in a packet header and a payload to be received after the sync word, an improved received data reproducing device proposed in the past is configured to detect data transition points and errors in the packet header and payload with a clock rate N times as high as the symbol rate of received data in the same manner as it deals with a sync word. The improved reproducing device can flexibly adapt to varying receipt conditions because it has a clock rate varying function for implementing the N times higher clock. Further, the improved reproducing device is configured to check data for errors, e.g. header errors and an FEC (Forward Error Code) to accurately receive the data, thereby providing the entire received packet with solidness and improved receipt characteristic. It follows that the improved reproducing device saves power at the same time if operated with the lowest, necessary clock rate satisfying the above conditions for the entire received packet.
However, the improved received data reproducing device stated above does not even suggest a function of determining an optimum clock frequency although indicating the adjustment to a clock rate N times as high as the symbol rate of received data. More specifically, although the clock rate adjusting function provides the reproducing device with flexibility, receipt characteristics are dependent on the index used to determine an optimum clock frequency. Stable operation is not achievable with a received data reproducing device if receipt characteristics are dependent on the index.